The present invention relates to centralising devices which are used for centralising pipes or tubes (sometimes called casings) in borings, generally earth borings. In particular, this invention relates to an improved blade carrying ring or collar for use in centralising devices.
Centralisers are known in which the blades are secured externally to the collar, for example by welding, clipping or slotting into or onto the collar. An arrangement is also known in which the blades are secured internally of the collar, the blade end being passed through the collar material which has been deformed in a U-shape to accept the blade end. It has been said that the above methods of securing the blades may have disadvantages in cost of manufacture or weakness in construction or problems in usage in that welding of the blade material may create undesirable stresses in the steel and collars made from deformed metal can be expanded.